1. Field of the Invention
The present invention relates to a co-plane capacitor structure having a signal electrode plate and an extension ground electrode plate both disposed on the same plane.
2. Description of Related Art
Along with the progress in electronic products, products with compact design and multiple functions have dominated the tendency on the market today, where, in particular, compacting parts and modules and lowering the numbers thereof become vital design criteria of new products. Today, the newly emerging embedded passive devices are able to substitute the conventional discrete passive devices, wherein by means of modern macromolecule compound material technology a passive device can be embedded inside a printed circuit board (PCB) by spreading, printing, pressing and etching processes.
In the embedded passive device, capacitors play an important role on dimension and price issues. However, the parasitic effect of conventional capacitors makes the capacitance varied nonlinearly, which reduces the resonance frequency of the capacitor so as to limit the frequency range thereof.
FIG. 1 is a diagram showing the electric characteristic of a capacitor. In FIG. 1, the abscissa represents operation frequency, the ordinate represents impedance of capacitor and the broken line represents resonance frequency Fr of capacitor. When the operation frequency is less that the resonance frequency Fr, the device behaves like capacitor, while when the operation frequency is greater than the resonance frequency Fr, the device behaves like an inductor.
In general, the larger size of a capacitor, the more serious of the parasitic effect thereof, which makes low resonance frequency Fr and narrow applicable range where the device behaving like a capacitor. In this regard, the U.S. Pat. Nos. 5,079,069, 5,155,655, 5,161,086 and 5,261,153 provide several plate capacitor structures suffered by lower resonance frequency and thus narrow applicable range. In addition, the U.S. Pat. Nos. 6,657,849 and 7,102,874 provide plate capacitor structures, which are suffered by limited resonance frequency problem as well.